Field of the Invention
A signal process technology is related, particularly to a signal process system dividing a biological impedance information into two portions, gain and phase, for detection by using resistive property and capacitive property of a biological tissue to be measured, and the method for the same, and a biological impedance detection device and element.
Descriptions of the Related Art
Biological impedance technology is an important technology in clinical medicine and biomedicine fields for nature determination or quantification of characteristic behaviors of various biological tissues to observe differences of different biological tissues from the characteristic behaviors essentially on the basis of existing electrical properties and frequency response properties of biological tissues themselves.
In early stage, the biological impedance technology is applied to fitness assessment of athletes, weight reduction, body fat meter and nutriology. In recent stage, it is mainly applied to monitor changes of status of blood, body fluid and different body tissues, for example, heart failure treatment, breath parameters measurement, cell property detection, nutrition status of patients, cardio-pulmonary function evaluation and biological impedance image. In recent years, the biological impedance technology is further applied to cancer detection for the comparison between normal cells and cancer cells as important references to determine whether or not cancer cells grow after surgery and to determine cancer recurrence or metastasis.
Compared to other detection methods (for example, isotope method, radioactive potassium tracking, ultrasonic wave, MRI (Magnetic Resonance Imaging) and CT (Computer Tomography) etc., the biological impedance is advantageous of easy operation, rapid analysis, high precision, and non-intrusion etc. Therefore, the biological impedance technology is an important development direction for biomedicine or clinical medicine now.
As mentioned above, the biological impedance technology can be applied to cancer detection. Particularly, for cancer postoperative patients, recurrent tumors still appear in original tumor sites for a certain proportion of patients as time goes by even though the clinical syndromes used to disappear through treatment after tumor cells are removed via surgery. Therefore, recurrence or transfer have to be followed up and monitored regularly either after surgery or treatment, and it is one of the current main directions to research how to implement such technology in implantable or portable biomedical electronic detection systems.
For previously various biological impedance technologies, the Wheatstone Bridge impedance detection technology proposed in the early years of the 19th century was used to measure impedance value of unknown impedance. In this technology, a galvanometer was placed in the middle to detect flow of current. As the reading from the galvanometer is zero, the potentials at two ends of the galvanometer are balanced and the impedance value of the object to be measured is known. This technology was advantageous of high resolution, accuracy and easy operation of device etc. However, more time was necessary to adjust balance of the bridge in measurement, such that it is not suitable for biological impedance that would change with time. Moreover, this technology itself consumed higher power and more hardware space was needed for implementation. Hence, this technology was not applicable to implantable or portable biological impedance detection system.
The more popular FRA (Frequency Response Analysis) technology used now utilizes PSD (Phase-Sensitive Detection), through which the information of both real part and imaginary part of impedance can be obtained directly. Principally, the original detection signal is used to perform demodulation with in-phase signal and quadrature-phase signal, respectively, to obtain real part and imaginary part signals of the impedance. This detection technology can provide higher accuracy and wider applicable frequency range, and achieve higher impedance detection speed compared to aforementioned Wheatstone Bridge technology. Moreover, it is capable of continuous detection insensitive to the change of the impedance of the object to be measured, which changes with time. Furthermore, its output signal is just the real part and imaginary part of the impedance of the object to be measured, such that it can restore real impedance via simple calculation.
However, the aforementioned biological impedance technology using PSD obtains the real part and imaginary part of the impedance from demodulation by two reference clock signals with different phases, so that an additional circuit is necessary to generate two reference signals, in-phase and quadrature-phase. The demodulation output result depends directly on the accuracy and the match of the two reference signals, which have different phases. Therefore, it is very important to generate reference signals which are accurate and have different phases. This would increase the complexity in implementing the circuit and increase the overall power consumption of the system. More hardware implementations are necessary for it to be an implantable or portable device. As a result, it is not applicable to implantable or portable device.
From above descriptions, the implantable or portable biological impedance detection system and the method for implementing the same are the technical subjects those skilled in the art are eager to explore currently.